The present invention relates to a method for producing a pressure sensor.
A method for producing a pressure sensor has been described, for example, in the printed document xe2x80x9cAdvanced Microsystems for Automotive Applicationsxe2x80x9d ""99, D. E. Ricken, W. Gessner, page 126. In the method described in this publication, a semiconductor pressure pick-up, which includes a semiconductor chip with pressure diaphragm mounted on a socket, is applied onto a lead grid, a so-called leadframe. A level section of the lead grid, a so-called diepad, is used as the mounting section of the semiconductor pressure pick-up. The semiconductor chip is subsequently connected to contact sections of the lead grid via bonding wires. In a method referred to as xe2x80x9ctransfer moldingxe2x80x9d, which is also called transfer forming, the semiconductor pressure pick-up is subsequently embedded in a housing made of mold compound. The pressure feed of the sensor can be effected from the top side of the semiconductor pressure pick-up, or through a pressure channel that is provided in the socket and the mounting section and is connected to the bottom side of the semiconductor pressure pick-up. When implementing the method, care should be taken when injection-molding around the semiconductor pressure pick-up that a pressure feed in the housing is kept free of mold compound. This is accomplished by a tool part which, in the injection molding die, is either pressed against the top side of the semiconductor pressure pick-up, or against the mounting section, depending upon whether the pressure feed is to be effected from the side of the semiconductor pressure pick-up facing away from the lead grid, or from the side facing the lead grid. After injection-molding around, the tool part is removed, causing an opening to remain in the mold compound which is used as a pressure feed.
Disadvantageous in the above-described method is that, when pressing the tool part, the mounting section of the lead grid can shift and a gap develops between the tool part and the mounting section. When injection-molding around, mold compound can get through the gap into the pressure feed and onto the diaphragm of the semiconductor chip, thereby impairing the functioning of the pressure sensor.
The known disadvantages are avoided by the method of the present invention. This is accomplished by clamping the mounting section within the injection molding die. For this purpose, the mounting section can have a region that extends laterally outwardly from the assembly surface of the semiconductor pressure pick-up and can be clamped simply and reliably in the injection molding die. The lateral enlargement of the mounting section necessitates only a slight alteration of the manufacturing method. Advantageously, by clamping the mounting section in the injection molding die, the mounting section is no longer able to give way when a tool part is pressed against the mounting section or the semiconductor pressure pick-up applied on the mounting section. Thus, the penetration of mold compound between the tool part and the mounting section or, if sealing was carried out on the top side of the semiconductor pressure pick-up, the penetration of mold compound between the tool part and the semiconductor pressure pick-up can be effectively prevented. The method is advantageously very simple and inexpensive to carry out and requires only insignificant alterations.
It is particularly advantageous if a region of the mounting section extending laterally from the assembly region of the semiconductor pressure pick-up is clamped between two die halves of the injection molding die, the die halves making contact with the top side and bottom side of the mounting section.
If a pressure channel is formed underneath the semiconductor pressure pick-up in the mounting section, the pressure channel can be covered particularly well if the entire bottom side of the mounting section facing away from the semiconductor pressure pick-up is covered by the tool part of the injection molding die. On the finish-produced pressure sensor, the side of the mounting section facing away from the semiconductor pressure pick-up is then not embedded in mold compound, and is freely accessible at the bottom side of the housing.